As one of optical information recording media capable of recording information (“recording”), reproducing information (“reproducing”), and erasing information (“erasing”) based on an irradiation of a laser beam, what is called a phase change type optical information recording medium has been known well. The phase change type optical information recording medium make use a phenomenon of phase transition between a crystalline and an amorphous phases or between the crystalline and the crystalline phases. Particularly, because of easiness in overwriting information (“overwriting”) by using a single laser beam, that is difficult to achieve in case of the optical magnetic recording, and because of a simple optical system of the apparatus used for recording/reproducing, the demand for the phase change type optical information recording medium has been increasing. As a result, CD-RWs, DVD-RWs, and DVD-RAMs have already been commercialized.
In general, if more information is to be recorded at a faster speed, then it becomes necessary to develop recording media having higher density and higher linear velocity.
Likewise, the linear velocity at which information can be recorded (“recording velocity” or “recording liner velocity”) with an optical information recording apparatus has also been increasing day-by day. At present, maximum recording linear velocities of different media belonging to the CD family are as follows. In case the CD-R, the maximum recording linear velocity is twelve times faster than that of the CD. In case the CD-RW, the maximum recording linear velocity is ten times faster than that of the CD. Moreover, the recording liner velocity of the CD-RW has always been higher than that of the CD-RW. For example, when the CD-RW had the recording velocity that is four times faster than that of the CD, the CD-R had a recording velocity of eight, ten or twelve times faster than that of the CD.
As a result, although a spindle, a semiconductor laser, and a control system that meet high recording velocity have been installed on the optical information recording apparatus, this optical information recording apparatus has recorded at a low velocity onto a CD-RW. This is mainly for the following reasons. The CD-RW stores information that indicates the standard recording linear velocity or the maximum recording linear velocity of the CD-RW. The optical information recording apparatus recognizes this information and then performs the recording based on a linear velocity that is in line with the read information. Therefore, it was not possible to achieve a higher recording velocity than the maximum recording linear velocity indicated by the information stored in the CD-RW.
Furthermore, the CD-RW disk also stores information indicating the minimum recording linear velocity. Recording on the CD-RW is performed at a recording linear velocity that is determined in such a manner that the recording linear velocity is between the minimum and the maximum recording linear velocities. Consequently, it is difficult in the optical information recording apparatus to perform matching at high-velocity recording. Therefore, such matching has never been realized.
In a phase change type optical information recording medium, usually, it is necessary to optimize a dislocation linear velocity of the medium so that it matches the recording linear velocity.
The dislocation linear velocity is defined as follows. As shown in FIG. 18, the optical information recording medium is rotated at various linear velocities. A semiconductor laser beam is traces a guide groove formed on the optical information recording medium. Because of the irradiation of the laser beam, a material of a recording layer in the optical information recording medium is heated to a melting point or above of that material. Reflectivity, i.e. the light intensity of the light reflected from the optical information recording medium, is measured. An example of the result of such a measurement are shown in FIG. 19. The linear velocity (shown by an arrow mark in FIG. 19) at which the reflectivity starts declining when the linear velocity is increased is called as the dislocation linear velocity.
As disclosed in detail in Japanese Patent Application Laid-open Publication No. 11-115313, it is important to control the dislocation linear velocity of the phase change type optical information recording medium, in order to the maintain the quality. Further, it has been disclosed in this publication, that the optimum dislocation linear velocity at two times to four times the linear velocity of the CD-RW (i.e. 2.4 to 5.6 m/s) is 2.5 to 5.0 m/s.
However, when the groove of the optical information recording medium has been narrowed, when the laser beam wavelength has been decreased, and when NA (number of apertures) have been increased for the purpose of increasing the density, the thermal properties of the optical information recording medium change drastically. Therefore, in order to carry out recording on to a phase change type optical information recording medium in a high-density and high-linear velocity area like two or more times the linear velocity of the DVD and eight or more times the linear velocity of the CD, the following becomes necessary. That is, it becomes necessary to examine the material of the recording layer, the layer structure of the medium, and conditions under which the medium is manufactured once more, and redesign the dislocation linear velocity that satisfies the factors such as the recording linear velocity, track pitch of the guide groove, wavelength of the laser beam, and NA.
Under the above circumstances, conventionally, the recording linear velocity of the CD-RW disk has been designed so as to be between the minimum and the maximum recording linear velocities. Moreover, the dislocation linear velocity is designed so as to be smaller than 0.85 times the maximum recording linear velocity. Thus, conventionally, it was not possible to increase the speed of recording.
As the material (“phase change recording material”) for forming the recording layer in the optical information recording medium, there are materials like GeTe, GeTeSe, GeTeS, GeSeS, GeSeSb, GeAsSe, InTe, SeTe, SeAs, Ge—Te—(Sn, Au, Pd), GeTeSeSb, GeTeSb, and AgInSbTe. Particularly, AgInSbTe has high sensitivity and has clear outline at an amorphous portion, and has been developed as a recording layer for a mark edge recording (refer to Japanese Patent Application Laid-open Publication No. 3-231889, Japanese Patent Application Laid-open Publication No. 4-191089, Japanese Patent Application Laid-open Publication No. 4-232779, Japanese Patent Application Laid-open Publication No. 4-267192, Japanese Patent Application Laid-open Publication No. 5-345478, and Japanese Patent Application Laid-open Publication No. 6-166266.)
Japanese Patent Application Laid-open Publication No. 3-231889 discloses a recording layer that is expressed by a general composition expression of a I·(III1-rVr)·VI2 type, where I represents a I-group element, III represents a III-group element, V represents a V-group element, and VI represents a VI-group element. However, according to this recording layer, a repetitive recording characteristic is not always sufficiently satisfactory.
Further, in the recording layer used in the optical information recording medium disclosed in Japanese Patent Application Laid-open Publication No. 4-191089, an improvement in erasing ratio and a high-speed recording can be achieved. However, there was a problem, in the disclosed technology, that when recording is performed repeatedly the recording characteristic (“repetitive recording characteristic”) gets degraded. Further, regarding an information recording medium disclosed in Japanese Patent Application Laid-open Publication No. 1-303643, it has been reported that it is possible to provide a medium having a high C/N ratio and repetitive recording characteristic and excellent preservation characteristic by employing a new crystalline structure. However, there is a drawback that the recording sensitivity and repetitive recording characteristic are not sufficient.
The portion where no information is recorded (i.e. the portion that is crystalline) of the recording layer used in an information recording medium disclosed in Japanese Patent Application Laid-open Publication No. 4-232779 has a structure that a stable phase (AgSbTe2) and an amorphous phase existing around this stable phase coexist. Therefore, although the disclosed medium had improved repetitive recording characteristic, a boundary of fine crystals is generated around the crystalline portion that became a cause of an occurrence of noise.
Existence of the boundary of fine crystals does not produce a seriously bad effect on the recording characteristic of an optical information recording medium that has a relatively low recording density like the CD-RW that uses a laser beam having a recording/reproduction wavelength of about 780 nm. However, the boundary of fine crystals becomes a hindrance in realizing a high-density recording of the DVD that uses a laser beam having a wavelength of 680 nm or below and has a recording density of about four times that of the CD-RW or the DVD-RW that have higher densities. Moreover, the problem of the repetitive recording characteristic remains unsolved.
A crystalline portion of the recording layer used in a recording medium disclosed in Japanese Patent Application Laid-open Publication No. 4-267192 has a structure that a phase of AgSbTe2 isolated from a uniform amorphous phase and other phase (a stable phase or an amorphous phase) coexist. When other phase is an amorphous phase, a problem similar to that of the information recording medium disclosed in Japanese Patent Application Laid-open Publication No. 4-232779 occurs. On the other hand, when the other phase is a stable crystalline phase, there is a problem that it is not possible to obtain satisfactory recording characteristic, as described later.
The technologies disclosed in Japanese Patent Application Laid-open Publication No. 5-345478 and Japanese Patent Application Laid-open Publication No. 6-166268 have problems similar to those described above. Namely, in an optical information recording medium that has a phase change recording material of an AgInSbTe system or this system with an expanded Ib group element, IIIb group element, Vb group element, and the VIb group element as a recording layer, there is no knowledge about a recording medium that prescribes coordination numbers of elements that constitute the recording layer. Therefore, there is no conventional techniques that make clear the roles of functions as a recording material of each constituent element. As a result, there is no detailed improvement carried out, based on a particular theory, in the repetitive recording characteristic of the AgInSbTe recording layer and information recording and erasing sensitivities.
Further, as phase change recording materials for forming the recording layer of the optical information recording medium, there are what are called chalcogen system alloy materials like GeTe, GeTeSn, GeTeS, GeSeS, GeSeSb, GeAsSe, InTe, SeTe, and SeAs, as disclosed in the specification of U.S. Pat. No. 3,530,441.
Further, for the purpose of improving stability and high-speed crystallization, there has been proposed a material having a GeTe system that is added with Au (Japanese Patent Application Laid-open Publication No. 61-219692), SnandAu (Japanese Patent Application Laid-open Publication No. 61-270190), and Pd (Japanese Patent Application Laid-open Publication No. 62-19490) respectively. Further, for the purpose of improving repetitive performance of recording/erasing, there have been proposed materials having specified composition ratios of GeTeSeSb, and GeTeSb (Japanese Patent Application Laid-open Publication No. 62-73438, and Japanese Patent Application Laid-open Publication No. 63-228433).
None of the above-described technologies has been able to satisfy all the characteristics required for a phase change type optical information recording medium. Particularly, there are important problems to be solved, such as the improvement in recording sensitivity and erasing sensitivity, the prevention of a reduction in an erasing ratio due to a remaining of a portion not erased at the time of an overwriting, and the increase in the life of a recorded portion and an unrecorded portion.
In the mean time, in Japanese Patent Application Laid-open Publication No. 63-251290, there has been proposed a recording medium that is equipped with a recording layer consisting of a multi-dimensional compound single layer having a crystalline state in substantially three or more dimensions. In this case, the multi-dimensional compound single layer having a crystalline state in substantially three or more dimensions is defined as a one that has a compound (for example, In3SbTe2) having a stoichiometric composition of three or more dimensions by 90 atom % or more in a recording layer. It has been disclosed that it is possible to improve the recording and erasing characteristics by using such a recording layer. However, this has a drawback in that the erasing ratio is small, and laser power required for erasing a recording has not yet been lowered sufficiently.
Further, in Japanese Patent Application Laid-open Publication No. 1-277338, there has been proposed an optical information recording medium that has a recording layer consisting of an alloy of a composition as represented by (SbaTe1-a)1-yMy. Here, 0.4≦a≦0.7, and Y≦0.2, and M is at least one element selected from a group consisting of Ag, Al, As, Au, Bi, Cu, Ga, Ge, In, Pb, Pt, Se, Si, Sn, and Zn. The base of this system is Sb2Te3. By adding Sb as a surplus, high-speed erasing and repetitive recording characteristic are improved. Moreover, by adding M, the high-speed erasing is further promoted. In addition, it has been disclosed that the erasing ratio due to a DC light is large. However, in this document, there is no description about the erasing ratio at the time of overwriting. Moreover, the recording sensitivity is insufficient. Inventors of the present invention carried out a study on the erasing ratio at the time of overwriting of the disclosed medium, and they found that non-erased portions were disadvantageously remaining.
Japanese Patent Application Laid-open Publication No. 60-177446 discloses a recording layer that uses an alloy of (In1-xSbx)1-yMy. Here, 0.55≦x≦0.80, and 0≦y≦0.20, and M is at least one element selected from a group consisting of Au, Ag, Cu, Pd, Pt, Al, Si, Ge, Ga, Sn, Te, Se, and Bi. Japanese Patent Application Laid-open Publication No. 63-228433 discloses a recording layer that uses an alloy of GeTeSb2Te3Sb (where Sb is surplus). However, none of the disclosed media posses satisfactory sensitivity and erasing ratio characteristics.
In addition, Japanese Patent Application Laid-open Publication No. 4-163839 discloses an optical information recording medium in which a recording thin film is formed by including N in a TeGeSb alloy. Japanese Patent Application Laid-open Publication No. 4-52188 discloses an optical information recording medium in which a recording thin film is formed by including at least one of components of a TeGeSe alloy as an a nitride in this alloy. Japanese Patent Application Laid-open Publication No. 4-52189 discloses an optical information recording medium in which a recording thin film is formed by making a TeGeSe alloy adsorb N. However, none of the disclosed optical information recording media posses satisfactory characteristics.
As mentioned above, it is required in case of the conventional optical information recording media to solve important problems such as the improvement in the recording sensitivity and the erasing sensitivity, the prevention of a reduction in an erasing ratio due to a remaining of a non-erased portion at the time of an overwriting, and the increase in the life of a recorded portion and an unrecorded portion.
In the mean time, in recent years, along a rapid popularization of the CD, there has been developed a compact disk into which data can be written only once (i.e. the CD-R). Such CD-Rs have already appeared in the market. However, in case of the CD-R, it is not possible to edit once the data is written. Therefore, when there is an input error in this CD-R, this disk cannot be used, and it has to be abandoned. Consequently, there has been desired a rewritable compact disk that can solve all these problems.
As a result of researches and developments to obtain such a disk, there has been developed a rewritable compact disk that utilizes an optical magnetic disk. However, the optical magnetic disk has drawbacks in that it is difficult to overwrite and that it is difficult to obtain compatibility between the optical magnetic disk and the CD-ROM or the CD-R. Therefore, the phase change type optical information recording medium is being researched because it has an advantage in securing compatibility in principle.
As researches made into a rewritable compact disk that uses the phase change type optical information recording medium, there are examples that have been announcedby Furuya and others in the lecture draft at the fourth phase change recording study symposium, 70 (1992), Jinno and others in the lecture draft at the fourth phase change recording study symposium, 76 (1992), Kawanishi and others in the lecture draft at the fourth phase change recording study symposium, 82 (1992), T. Handa and others in Jpn. J. Appl. Phys., 32 (1993), Yoneda and others in the lecture draft at the fifth phase change recording study symposium, 9 (1993), and Tominaga and others in the lecture draft at the fifth phase change recording study symposium, 5 (1993). However, none of them have sufficiently satisfied a total performance including a securing of compatibility with the CD-ROM or the CD-R, recording and erasing performance, recording sensitivity, possible repetitive number of rewriting, number of reproduction, preservation stability, etc. These drawbacks are mainly due to a composition of recording materials and a low erasing ratio attributable to a structure.
Because of the above reasons, it has been expected to develop phase change recording materials that are suitable for high-sensitivity recording and erasing, and to develop a phase change type compact optical information recording medium having high performance and capable of rewriting.
The present inventors have found and proposed that an AgInSbTe system recording material is the material that solves almost all the drawbacks. As representative examples of the publication by the present inventor there are: Japanese Patent Application Laid-open Publication No. 4-78031, Japanese Patent Application Laid-open Publication No. 4-123551, H. Iwasaki and others in Jpn. J. Appl. Phys, 31 (1992) 461, Ide and others in the lecture draft at the third phase change recording study symposium, 102 (1991), and H. Iwasaki and others in Jpn. J. Appl. Phys, 32 (1993) 5241.
The Orange Book part III (version 1.0) was published in October 1996 as a standard of a rewritable compact disk (CD-RW). As the Orange Book part III (version 1.0) is a standard of a CD-RW two-time linear velocity recording (2.4 to 2.8 m/s), a recording time becomes too long based on this low linear velocity. Therefore, an advent of a high-speed recording rewritable compact disk has been expected.
In the mean time, various kinds of recording compensation systems have been disclosed as systems for improving the quality of recording signals in the phase change type recording system.
For example, Japanese Patent Application Laid-open Publication No. 63-266632 discloses, that a system for recording an amorphous mark by using a pulse string is effective in a PWM recording using a recording film having a high crystallization speed.
Further, Japanese Patent Application Laid-open Publication No. 63-266633and U.S. Pat. No. 5,150,351 disclose, that jitter is improved by restricting a positional fluctuation of a mark edge, by increasing laser energy at the head or tail of a pulse string or by increasing an irradiation time. Further, as described in Japanese Patent Application Laid-open Publication No. 63-29336, there has been known a method of scanning while irradiating an optical spot like a laser beam onto an optical disk in an optical disk recording apparatus, and recording an information signal onto the optical disk by strongly or weakly modulating the optical spot like a laser beam with the information signal. There has also been known a method of reproducing an information signal recorded on an optical disk, and monitoring an amplitude of a reproduction signal and a length of a recording mark, thereby to adjust recording conditions like recording optical power and a width of a recording optical pulse in an optimum state, and set these conditions.
Further, Japanese Patent Application Laid-open Publication No. 9-138946, Japanese Patent Application Laid-open Publication No. 9-138947, and Japanese Patent Application Laid-open Publication No. 9-219021 have disclosed the following. In the case of recording information onto an information recording medium according to a PWM recording system, a recording wave at the time of recording or rewriting a 0 signal having a signal width n×T after modulation (where T is a clock time) is a continuous electromagnetic wave having a power level e. Then, a recording wave pulse string at the time of recording or rewriting a 1 signal having a signal width n×T after modulation is an electromagnetic wave pulse string that has a pulse portion fp having a time width x and a power level ‘a’, a multi-pulse portion mp in which a low-level pulse of a power level b having a time width T in total and a high-level pulse having a power level c alternately continue by (n−n′) times in total at a duty ratio y, and a pulse portion op having a time width z and a power level d, where x, y, and z are in relationships of T×0.5≦x≦T×2.0, 0.4≦y≦0.6, and T×0.5≦z≦T, n′ is a positive integer of n′≦n, and a & c≧e≧b & d.
Based on the conventional techniques, there have been substantial improvement in the quality of a recording signal and the stability at the time of repeating an overwriting, and improvement in reliability and general applicability. However, in recent years, a technique for making it possible to record at a plurality of linear velocities (a multi-speed recording) in one information recording medium has been required in a rewritable information recording medium, particularly, in the phase change type optical information recording medium.
Further, a high-speed recording has also been required, and a CAV recording that is advantageous in a high-speed recording has also been required. The technologies in the above-described Japanese Patent Application Laid-open Publication No. 9-138946, Japanese Patent Application Laid-open Publication No. 9-138947, and Japanese Patent Application Laid-open Publication No. 9-219021 have not been able to meet these technical requirements. For example, it has been tried to carry out a recording at an eight-time linear velocity and at a ten-time linear velocity respectively, based on the recording strategy having fp, mp, and op where it is possible to record at four times the linear velocity of the CD. In this case, it has not been possible to obtain sufficient signal quality in the recording at the eight-time linear velocity and at the ten-time linear velocity respectively. Furthermore, there has been a problem of degradation in the signal quality in the overwriting at a different recording linear velocity. For example, there has been a problem of degradation in the signal quality in the case of overwriting at ten times the linear velocity of the CD on a portion recorded at four times the linear velocity of the CD, and overwriting at four times the linear velocity of the CD on a portion recorded at ten times the linear velocity of the CD. Moreover, there has also been a problem of degradation in the signal quality in the overwriting based on a different recording system, such as overwriting in a CAC recording at a CLV recorded portion, and an overwriting in a CLV recording at a CAV recorded portion.